1. Field of the Invention
The present disclosure relates to a fixing apparatus for fixing a toner image onto a recording material, and an image forming apparatus that is equipped with the fixing apparatus and utilize an electrophotographic method or an electrostatic recording method, such as a printer, a copying machine, a facsimile, a multifunction peripheral, or the like.
2. Description of the Related Art
In such an image forming apparatus, an image forming unit forms a unfixed toner image onto a sheet of a recording material (hereinafter, also referred to as paper), and then a fixing unit (fixing apparatus) fixes the toner image as a fixed image.
As for the fixing unit, various types have been discussed. Among those, in recent years, an environmentally-friendly power-saving fixing type has been increasingly in demand. Currently, a heating-type fixing unit has been in practical use. In an image forming apparatus, such a heating-type fixing unit uses a heating member having a low heat capacity such as a ceramic heater, a belt having a low heat capacity, and a pressure roller that pressurizes and drives the belt, so that the image forming apparatus at low temperature can be rapidly heated.
However, in the apparatus having the heating-type fixing unit, when small size sheets pass there through continuously, a surface of an area through which sheets do not pass (i.e., a non-sheet-passing area) of the belt is heated to an excessively high temperature. This is because, during the continuous passing of small size sheets, the non-sheet-passing area where the recording materials do not pass continues to receive heat without removal by the recording materials.
The phenomenon is called edge temperature rise at a fixing unit or temperature rise at non-sheet-passing area. An excess edge temperature rise may result in hot offset or heat damage of members of the apparatus.
In addition, at the start of continuous printing after warming-up of the apparatus from low temperature by the fixing unit, water vapor is given off from sheets that pass the fixing unit, which may lead to occurrence of condensation at a pressure roller that has not reached a temperature greater than its dew point. The condensation at the pressure roller decreases friction between the pressure roller and a belt facing thereto. The decreased friction may cause an issue of slippage between the pressure roller and the belt (hereinafter, referred to as condensation slippage).
Among the above issues, as for the temperature rise at non-sheet-passing area, Japanese Patent Application Laid-Open No. 2008-32903 discusses a resolution. The resolution uses a cooling fan that supplies cooling air toward a non-sheet-passing area, while avoiding temperature rise at the non-sheet-passing area by adjusting the length of an air outlet port of the fan in its width direction, according to the width of a recording material to be used. As for the condensation slippage, Japanese Patent Application Laid-Open No. 2008-116858 discusses a technique for using a fan disposed below a fixing apparatus to avoid condensation. The fan operates as a pressure roller operates, so that any condensation in the fixing apparatus can be avoided.
These structures for avoiding temperature rise at a non-sheet-passing area and condensation slippage, however, require a plurality of fans only for a single fixing unit. The increase in the number of the fans swells the number of power sources, electric circuits, control circuits, fan ducts, and covers to be used, according to the number of the fans. The increase in the total number of the components may increase costs and sizes of a fixing unit and an image forming apparatus equipped with the fixing unit.
In recent years, such a fixing unit and an image forming apparatus equipped with the fixing unit have been demanded to have characteristics of power saving, print productivity (e.g., time saving in printing of one sheet), down-sizing of apparatus body, and low cost. To meet the demand to the maximum extent, decrease in the number of fans is an essential key.